I am using this in another series Im doing in pre-smithy, but thought Id share it.
some card with activated ability that is powerful
do the powerful ability, increase the cost of this ability on all copies of this card by
until end of turn
in other words, say you have a card that deals 8 damage to a target creature for 3 fire. When you use it, all other copies of this 'fireweaver creature or whatever, then have the cost of 4 fire to use the ability. and if used again, the rest go to 5 fire, etc. it resets at the end of turn. Or you could have it go down one per turn.
anyway, just an interesting mechanic Im using in something Im working on